The present invention relates to exothermic welding and an improved assembly, weld metal cartridge and igniter therefor.
Exothermic welding has been employed in the past as an effective method of welding two or more members together which may be copper and/or steel, such as cables to cables, cables to ground rods, cables to steel surfaces including plates and pipes, cables to bus bars, cables to rebar and the like. Such exothermic welding eliminates the need for an outside source of heat or power and produces a permanent, corrosion resistant weld which cannot loosen and does not increase electrical resistance.
In exothermic welding a particulate weld metal is employed which is a mixture of copper oxide and aluminum which, when ignited, produces the following chemical reaction:3Cu2O+2Al→6Cu+Al2O3+heat(4600° F.)
To accomplish such welds the members to be welded together are positioned adjacent to each other utilizing a weld cavity in a mold formed of a material, such as graphite, which is capable of withstanding the extremely high temperatures of the exothermic welding process. Another ignition cavity in the mold contains a loose particulate weld metal which is to be ignited to initiate the welding process. A metal disk, which typically is a tin plated steel, is first positioned in the ignition cavity to prevent the loose particulate weld metal from flowing into the welding cavity in which the materials are to be welded together prior to ignition. The loose particulate weld metal is then poured into the ignition cavity, and the mold cover is closed. In order to initiate ignition, a spark generator ignites the loose particulate weld metal which melts in the ignition cavity to melt the metal disk and the molten weld metal flows from the ignition cavity into the weld cavity to weld the members together.
In another prior exothermic welding procedure as disclosed for example in U.S. Pat. No. 6,994,244, a weld metal cartridge comprising a container which contains the weld metal is placed in the ignition cavity of the mold, and an igniter formed of electrical conductors is positioned in the weld metal in the container. When an electrical current is passed through the conductors, the igniter heats to ignite the weld metal, and the molten weld metal flows from the ignition cavity into the weld cavity to weld the members together. In this procedure, the container may be formed of a metal, such as copper, which also melts with the weld metal and flows with the molten weld metal to the weld cavity. The container may also be formed of other metals, such as steel. However, even though the steel bottom of the container may achieve a sufficient temperature to melt when the weld metal is melted, the steel side walls may not, thereby leaving a residue which must be removed from the ignition cavity before the mold can be reused to perform another welding procedure.
In still another prior exothermic welding procedure, ignition of the loose particulate weld metal in the ignition cavity is initiated by first igniting a starting powder which ignites quickly and at a lower ignition temperature than the ignition temperature of the weld metal. This starting material may be a more finely ground form of the weld metal and may be located in a depression in the cover of the mold where it can be ignited by a spark from a flint igniter. After ignition, the molten starting material flows through the cover and into the weld metal in the ignition cavity of the mold to ignite and melt the weld metal in the ignition cavity.
Smokeless exothermic welding procedures are also currently available for exothermic welding in clean room environments. In such smokeless procedures a filter is employed with the mold to trap most of the emissions created in the exothermic welding process while allowing the heated air to escape through the filter.
It would be desirable if an exothermic welding mold existed which was capable of accommodating at least each of these several exothermic welding procedures as well as others, and which would avoid the need for maintaining an inventory of different molds in order to enjoy the specific advantages of each procedure.
It would also be desirable if the mold was capable not only of accommodating the performance of each of these exothermic welding procedures, but could also accommodate the smokeless exothermic welding procedures discussed above.
In one principal aspect of the present invention, an exothermic welding assembly, comprises a mold formed of a material which withstands exothermic welding temperatures and which has an elongate axis. The mold includes a first portion having a first cavity therein for positioning at least two members adjacent each other which are to be exothermically welded together, and a second portion comprising a mold cover. A second cavity is present in the mold for containing a weld metal. The second cavity communicates with the first cavity and has a first vent passage extending therefrom to the exterior of the mold to vent gases from the second cavity. A depression is located in the mold cover for containing a starting material for the initiation of the reaction of the weld metal. The depression in the mold cover opens to the top of the mold cover, and a second passage extends between the depression and the second cavity in the mold to communicate the starting material when ignited with the weld metal in the second cavity. A third passage is also associated with the mold and which extends at a substantial angle to the elongate axis from a side of the mold and toward the elongate axis of the mold and the depression.
In still another principal aspect of the present invention, in the assembly the third passage extends through the cover and from the side of the mold into the depression, and the third passage is constructed and arranged to receive an electrical igniter and contain it in the third passage so that the igniter can extend from outside of the mold into the depression.
In another principal aspect of the present invention, in the assembly the third passage extends along the top of the cover and from the side of the mold toward the depression, and the third passage is constructed and arranged to receive an electrical igniter and contain it in the third passage so that the igniter can extend from a side of the mold into the depression.
In still another principal aspect of the present invention, the assembly includes a fourth passage which extends at a substantial angle to the elongate axis from a side of the mold and toward the elongate axis between the first portion of the mold and the cover and from the side of the mold and into the second cavity, and the fourth passage is also constructed and arranged to receive an electrical igniter and contain it in the fourth passage so that the igniter can extend from outside of the mold into the second cavity and the weld metal therein.
In still another principal aspect of the present invention, the assembly includes a container in the second cavity in the mold which contains the weld metal, and an electrical igniter has one end positioned in the container and in the weld metal therein, and the other end extends laterally from the container and through the fourth passage to the outside of the mold.
In still another principal aspect of the present invention, the container includes a cover on the container, and the igniter extends laterally from the container and from beneath the cover.
In still another principal aspect of the present invention, the assembly includes a filter in the mold between the second cavity and the first vent passage.
In still another principal aspect of the present invention, a weld metal cartridge for exothermic welding comprises a container having a top, a side wall and a bottom with the side wall and bottom defining a chamber therein. A particulate weld metal is in the chamber, and a cover covers the top and retains the particulate weld metal in the chamber and the said side wall of the container is positioned relative to the particulate weld metal and is formed of a material so that the side wall melts with the particulate weld metal during the welding procedure. A plate of material is located adjacent the bottom which is formed of a material which melts at a higher temperature than the material of the side wall.
In still another principal aspect of the present invention, the material of the side wall comprises copper and/or the plate comprises steel, and the plate may be a disk which covers a substantial area of the bottom.
In still another principal aspect of the present invention, the container includes a bottom wall and the disk is fixed to the bottom wall.
In still another principal aspect of the present invention, an electrically conductive igniter has one end thereof in the chamber of the container beneath the cover and adjacent the weld metal, and an opposite end of the igniter extends from the container and from beneath the cover, whereby the end of the igniter in the container ignites the weld metal upon passage of an electrical current through the igniter.
In still another principal aspect of the present invention, an igniter for igniting a particulate exothermic weld metal, comprises a pair of flat, longitudinally extending electrical conductor strips, and a sheet of insulation is laminated between the electrical conductor strips to insulate the electrically conductive strips from each other. An ignition element comprising a filament is located adjacent one end of the electrical conductor strips and electrically connected to the strips, and the filament is formed of a material which heats substantially when electricity is passed therethrough to a temperature sufficient to ignite the exothermic weld metal. The other end of the electrical conductor strips is adapted to be coupled to a source of electrical power sufficient to cause the filament to heat to ignite the particulate exothermic weld metal.
In still another principal aspect of the present invention, the filament material is tungsten and/or the insulation is an aromatic polyamide.
In still another principal aspect of the present invention, at least one positioning tab is located adjacent the one end of one of the strips for positioning the filament prior to ignition of the particulate exothermic weld metal, and the positioning tab may be constructed and arranged to couple the igniter to the top of a container for containing the particulate exothermic weld metal.
In still another principal aspect of the present invention, at least two positioning tabs are spaced from each other on one end of one of the strips and they may be constructed and arranged to couple the igniter to the top of a container for containing the particulate exothermic weld metal.
In still another principal aspect of the present invention, one of the electrical conductor strips is narrower in width than the other.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.